Sexless for a million years, stick bugs elude extinction

Jul 19, 2011

The genus Timema, a species of walking stick insect, has been asexual for over a million years and has escaped extinction. (Photos by Bart Ziglstra)

(PhysOrg.com) -- Simon Fraser University biologists say a species of stick insect found to be celibate for 1.5 million years raises questions about why these particular lineages have escaped extinction thus far.

In a paper published in the journal Current Biology, SFU biology professor Bernie Crespi and Tanja Schwander, a former post-doctoral researcher in Crespis lab, say the persistence of the insect, known as the genus Timema, is most likely because of a combination of genetic and ecological processes.

The researchers used a series of genetic analyses to show that several clonal or cloned lineages in the stick insect, mainly found in the western U.S., have persisted for more than one million generations. The finding raises questions around why theyve eluded extinction to date and has allowed researchers to address the consequences of long-term clonality.

Why most species reproduce sexually is a big question in evolutionary biology, because at least theoretically, it appears that clonal reproduction would be more efficient, says Schwander, currently a fellow in evolutionary genetics at the University of Groningen, in the Netherlands.

The genus Timema, a species of walking stick insect, has been asexual for over a million years and has escaped extinction. (Photos by Bart Ziglstra)

Many genetic and ecological mechanisms have been suggested that could result in disadvantages of clonal reproduction. One common expectation of these mechanisms is that reproductive advantages gained by new clonal lineages will be quickly eroded over time.

Their genetic studies led the researchers to determine the last point in time the insect line engaged in sex. Their findings add to the growing evidence that asexuality does not always result in the rapid extinction of a lineage and are the basis of their ongoing research.

SummaryAsexuality is rare in animals in spite of its apparent advantage relative to sexual reproduction, indicating that it must be associated with profound costs. One expectation is that reproductive advantages gained by new asexual lineages will be quickly eroded over time. Ancient asexual taxa that have evolved and adapted without sex would be scandalous exceptions to this rule, but it is often difficult to exclude the possibility that putative asexuals deploy some form of cryptic sex, or have abandoned sex more recently than estimated from divergence times to sexual relatives. Here we provide evidence, from high intraspecific divergence of mitochondrial sequence and nuclear allele divergence patterns, that several independently derived Timema stick-insect lineages have persisted without recombination for more than a million generations. Nuclear alleles in the asexual lineages displayed significantly higher intraindividual divergences than in related sexual species. In addition, within two asexuals, nuclear allele phylogenies suggested the presence of two clades, with sequences from the same individual appearing in both clades. These data strongly support ancient asexuality in Timema and validate the genus as an exceptional opportunity to attack the question of how asexual reproduction can be maintained over long periods of evolutionary time.

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User comments : 15

Why most species reproduce sexually is a big question in evolutionary biology,

And it will remain an unsolvable enigma for a long, long time because there is a meaning enshrouded within sex that cannot be attained by purely evolutionary reasoning.Evolutionary thinking cannot answer the question of "WHY is there sex?" Never mind even getting to explain as to HOW is it that there is sex because it's an impossibility of the first kind, an either all or nothing proposition. Or to put it more obscurely, it's irreducibly complex.The "two shall become one" is a mystery to those who will not believe in Special creation.

i would think that stickbugs are so succesfull in their camouflage they have high survivabillity against predation, as for the danger of similar clonal dna against parasites, i would think that because stickbugs are vegetarian, they might extract chemicals or gene-switchers from the sexually evolving plants they feed on against bugs?

The other big question is why has there been evolutionary stasis[oxymoron if ever there was one] in this case - as in the now increasingly more frequent discovery of living fossils.This is the problem with evolution - highly rapid mutation rates are required to produce the impossibly big diversity we find around us and yet we find this conundrum of creatures having survived for millions of years without ANY change. Begs the question of what is evolution? All things to all people, and then some. Whenever an exception is found that clearly discredits the mythical evolution, another adhoc assumption is brought up to explain it. No matter that that assumption then contradicts some basic tenets. The all-shape all-forms chameleon that is evolution lives on...

Why most species reproduce sexually is a big question in evolutionary biology, because at least theoretically, it appears that clonal reproduction would be more efficient, says Schwander, currently a fellow in evolutionary genetics at the University of Groningen, in the Netherlands.

Schwander you go ahead and clone yourself ; let's see if you can do this. No help from nobody just yourself. And why to clone or reproduce???

This article kind of reminds me of a part from the movie called "Master and Commander" when Russel Crow says "let me guess: it's a stick"! hahaha!

You are right about the issue of how sex is irreducible complexity: it's no less than a chicken or egg first problem, except for in this case they both have to come about at the same time! Tuff one to explain away!

As usual, kev is in first, trying to pretend that this is a problem for evolutionary theory, using imperative statements with no backup, no training, and no research.

Hey kev, come up with any evidence for the existance of your magic sky fairy yet? Didn't think so. How about some evidence that your collected fairy tales were dictated by said fairy? Didn't think so. How about some evidence (or even a logical argument) showing how any shortcomings in Evolutionary theory would automatically prove your particular delusion by default? Didnt't think so. Still waiting...

Your first comment is on point it states a problem and it is a question that evolution as a paradigm cannot answer. It is these types of questions that eventually change a paradigm.

Your second comment is baseless. It is a given fact to some of us that there have been a few (5) massive extinctions on this planet. From those there has always been a rebound. I offer no explanation as to why they happened. But that speciation and specialization took place is hard to argue, for me at least, and I think the fossil record while incomplete is probably close to accurate portrayal of the periods.

Having very few species that deviate from the norm is not a detriment to evolution but rather proves the rule, that cloning is in fact very very rare. But to your point evolution has no way of answering why or how sex developed - but it can answer why sex has been successful.

@ everyone else

Kevin is Christian and so am I - some questions are about flaws in logic - nothing else

While everyone jumped on the second comment the Great question that was posed initially was ignored - because it is HARD. There is no basis for sex. While we accept male and female as two genders of one species - the fact that they need each other and are by instinct attracted to each other is a wild idea. You accept sex because you've thought about it your entire life --- but going from a single celled cloning organism to NEEDING DNA imput from an outside source is WILD. How the heck did that happen... and this organism that started needing sex almost has to common to every thing else that uses that mechanism. Because it is wild. Now I know that eyes or wings can develop seperately on evo paths but can we prove that sex developed independently over SO many species?? has anyone even ever asked that question?

I just thought of something. The Egyptians were obviously not god's chosen people. How could they have been so successful to build something as great as the Giza complex, which still exists to this day, yet the Israelites can't keep their temples up for more than a few centuries? With the grace of god that shouldn't be a problem should it? Why haven't the pyramids crumbled? They stand in defiance of Yahweh.

Sex is an irreducible complexity problem the same way the eye is: It's not, except to creotards who are trying to manufacture a problem. Like the eye, there exists every stage from simple gene-swapping through mutual hermaphroditic dna exchange (snails for one) to male-female setups, and quite a few "fuzzy" in-betweens. But trust xians to squint, cover their ears, and yell "irreducible complexity! irreducible complexity!" as if the chant will make it so.

Ditto the explanation for sex. Really? How many articles have been written ON THIS WEBSITE about the arms race between host and parasite. Christ, that idea is probably almost 50 years old. This is as bad as the creotards continuing to chant "there are no fossils!".

Kev and others, I'm sure it makes you feel really really good about yourselves to go out and show them pagans what's what, but in the real world (where most of us exist), you just come across as uninformed (at best) idiots (at worst). But hey, I'm fine with that.

eye -- development of an organ that occurred independently across many different species. The human eye and its genes have NO RELATION AT ALL genetically to many other species' eyes - this implies that this organ evolved in a totally separate and isolated way.

sex -- is a mechanism for reproduction that involves sharing of genes from at least two separate entities, for those genes to fuse and create a new unique individual of the same species. Sex/fertilization seems to work EXACTLY THE SAME across ALMOST ALL species that produce sexually, one partner is either a carrier or producer of an egg that receives foreign DNA to complete the offspring.

the only thing that hints that his may be easy or a normal factor is because almost everything on earth does it.

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